Applications provides all installed programs.
Launching an application
Activate Kupfer and type an abbreviation of the application name
Press Return to launch the application.
Opening a file with a specific application
Select a file in Kupfer
Type Tab and select the action Open With...
Type Tab to select the third (indirect object) pane and in it, select the application to open the file with.
The action Open opens files and folders with the registered default application for that specific file type. This can be configured using the action Set Default Application....
The file type associations are provided by the desktop environment, and modifying them here will modify them on the desktop as well. This may not be true when not using GNOME or XFCE.
Selecting default application for a file type or folders
Select a file or folder in Kupfer
Type Tab and select the action Set Default Application...
Type Tab to select the third (indirect object) pane and in it, select the application to always open the file type with.
The configuration option Applications for Desktop Environment in the plugin's information pane in Kupfer Preferences determines how Kupfer should act with regard to the desktop environment configuration—certain applications request not to be shown depending on which desktop environment is used.
The default setting is blank which means that it will use the environment variable XDG_CURRENT_DESKTOP to identify the desktop environment automatically.